Lightweight sandwich structures (e.g., a structure including a core “sandwiched” between two facesheets) are used for a variety of purposes including heat exchange, advanced armor applications, high impact/low weight applications, etc. In some embodiments, it may be beneficial to form lightweight sandwich structures into particular curvatures that conform to a surface where the material will be used. In some instances, forming a sandwich structure into a particular shape may require costly manufacturing techniques.
Generally, the materials used for lightweight sandwich structures dictate how the structure is formed and whether it can be formed to have complex curvatures. Existing materials used as cores for lightweight sandwich structures include foams, honeycomb, and metal lattice structures. Each of these materials has limitations in its ability to conform to particular curvatures.
Foams can be either open-cellular or closed cellular and are available in a variety of materials including, but not limited to, polymers, metals, and ceramics. Open-cellular foams generally have limited strength and stiffness, which limits their usefulness in a variety of applications. Open-cellular foams also have tortuous, non-uniform paths for fluid flow, in which high pressures are often used to force fluid through the structure. Closed-cellular foams have greater strength and rigidity than open-cellular foams, making them more suitable as cores for sandwich structures. However, closed-cellular foams do not permit fluid to freely flow through the material, which limits their usefulness in applications where fluid flow is required, such as heat transfer applications. Generally, machining is used to form foam into a particular curvature.
Honeycomb structures are also available in a number of different materials including, but not limited to, aluminum, Nomex®, and thermoplastic polymers. Generally, honeycomb structures are closed-cellular. In order to achieve a particular curvature with a honeycomb structure a specific corresponding unit cell shape is generally used. This approach may work for a structure requiring a single radius of curvature; however, it is less effective for complex curvatures which have more than one radius of curvature.
Metallic lattice structures have good strength and stiffness properties and may also function as fluid heat exchanges because the structures allow low pressure drop fluid flow through the material. However, to form a metal lattice structure into a particular curvature, the structure is generally plastically deformed or machined.
As such, there is a need for a lightweight structure that can be easily formed to have a particular curvature without resorting to pre- or post-production manufacturing, which may be expensive or may damage the structural integrity of the sandwich structure.